/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformMisc.h
Gets a string representing the numeric OS version (as opposed to a translated OS version that GetOSVersions returns). The returned string should try to be brief and avoid newlines and symbols, but there's technically no restriction on the string it can return. If the implementation does not support this, it should return an empty string.
static [FString](API\Runtime\Core\Containers\FString) GetOSVersion()